The present invention relates to an improved etching machine for making a flexible block which can be used for printing in flexography, typography or dry offset, and the corresponding process for separating the components of the etching bath contained in the machine.
It is known that it is possible to obtain a block for flexography or typography by exposing a plate formed of a photopolymer sensitive to ultraviolet radiation. A negative film is used to expose those regions of the photopolymer which are to come into relief on the finished block to the radiation. This constitutes what is generally referred to as the exposure step.
The radiation cures the exposed regions and the material from the protected surface is subsequently removed by brushing the material from the plate using plane or rotary brushes or by spray nozzles using water plus a detergent which acts as wetting agent. The operation is continued until the regions which have been exposed are sufficiently in relief. This constitutes what is generally referred to as the etching step.
During the etching step, the water plus the detergent becomes loaded, then saturated with dissolved and/or suspended polymer particles. The etching bath therefore needs to be changed regularly.
A problem arises regarding the saturated aqueous solution, which needs to be treated in a treatment device independent of the etching machine. In particular, since treating the solution never allows all the polymer particles to be removed, a problem arises in terms of environmental protection.
A solution to this problem is proposed in FR 2,709,192. To this end, a device and a process are disclosed for preparing photopolymer blocks which can be used for printing in flexography, typography or dry offset, which includes the polymerization of desired regions by exposure to ultraviolet radiation, etching of the regions by exposure to ultraviolet radiation and etching of the unpolymerized regions by immersion and brushing in an etching vat. The disclosed device and process includes automatic and continuous separation of the etching bath, with the liquid obtained during such separation being automatically reinjected into the etching tank.
Even though the process and the device described in FR 2,709,192 are satisfactory, experience has shown that the filter belt which receives and filters the solution and which is discharged to a storage vat, can contain a significant quantity of contaminated aqueous solution. This contributes to the environmental problem described above.